CosmologyCosmology (from the Greek κόσμος, kosmos "world" and
-λογία, -logia "study of") is the study of the origin, evolution,
and eventual fate of the universe.
Physical cosmologyPhysical cosmology is the
scientific study of the universe's origin, its large-scale structures
and dynamics, and its ultimate fate, as well as the scientific laws
that govern these areas.[2]
The term cosmology was first used in English in 1656 in Thomas
Blount's Glossographia,[3] and in 1731 taken up in Latin by German
philosopher Christian Wolff, in Cosmologia Generalis.[4]
Religious or mythological cosmology is a body of beliefs based on
mythological, religious, and esoteric literature and traditions of
creation myths and eschatology.
Physical cosmologyPhysical cosmology is studied by scientists, such as astronomers and
physicists, as well as philosophers, such as metaphysicians,
philosophers of physics, and philosophers of space and time. Because
of this shared scope with philosophy, theories in physical cosmology
may include both scientific and non-scientific propositions, and may
depend upon assumptions that cannot be tested.
CosmologyCosmology differs from
astronomy in that the former is concerned with the
UniverseUniverse as a whole
while the latter deals with individual celestial objects. Modern
physical cosmology is dominated by the
Big BangBig Bang theory, which attempts
to bring together observational astronomy and particle physics;[5]
more specifically, a standard parameterization of the
Big BangBig Bang with
dark matter and dark energy, known as the
Lambda-CDMLambda-CDM model.
Theoretical astrophysicist David N. Spergel has described cosmology as
a "historical science" because "when we look out in space, we look
back in time" due to the finite nature of the speed of light.[6]

Axis scale: billion years
Also see:
HumanHuman timeline and Life timeline

PhysicsPhysics and astrophysics have played a central role in shaping the
understanding of the universe through scientific observation and
experiment.
Physical cosmologyPhysical cosmology was shaped through both mathematics and
observation in an analysis of the whole universe. The universe is
generally understood to have begun with the Big Bang, followed almost
instantaneously by cosmic inflation; an expansion of space from which
the universe is thought to have emerged 13.799 ± 0.021 billion years
ago.[7]
CosmogonyCosmogony studies the origin of the Universe, and cosmography
maps the features of the Universe.
In Diderot's Encyclopédie, cosmology is broken down into uranology
(the science of the heavens), aerology (the science of the air),
geology (the science of the continents), and hydrology (the science of
waters).[8]
Metaphysical cosmology has also been described as the placing of man
in the universe in relationship to all other entities. This is
exemplified by Marcus Aurelius's observation that a man's place in
that relationship: "He who does not know what the world is does not
know where he is, and he who does not know for what purpose the world
exists, does not know who he is, nor what the world is."[9]
Physical cosmology[edit]
Main article: Physical cosmology
Physical cosmologyPhysical cosmology is the branch of physics and astrophysics that
deals with the study of the physical origins and evolution of the
Universe. It also includes the study of the nature of the
UniverseUniverse on
a large scale. In its earliest form, it was what is now known as
"celestial mechanics", the study of the heavens. Greek philosophers
Aristarchus of Samos, Aristotle, and
PtolemyPtolemy proposed different
cosmological theories. The geocentric
Ptolemaic systemPtolemaic system was the
prevailing theory until the 16th century when Nicolaus Copernicus, and
subsequently
Johannes KeplerJohannes Kepler and Galileo Galilei, proposed a
heliocentric system. This is one of the most famous examples of
epistemological rupture in physical cosmology.

Evidence of gravitational waves in the infant universe may have been
uncovered by the microscopic examination of the focal plane of the
BICEP2BICEP2 radio telescope.[10][11][12]

When
Isaac NewtonIsaac Newton published the Principia Mathematica in 1687, he
finally figured out how the heavens moved. Newton provided a physical
mechanism for
Kepler's lawsKepler's laws and his law of universal gravitation
allowed the anomalies in previous systems, caused by gravitational
interaction between the planets, to be resolved. A fundamental
difference between Newton's cosmology and those preceding it was the
Copernican principle—that the bodies on earth obey the same physical
laws as all the celestial bodies. This was a crucial philosophical
advance in physical cosmology.
Modern scientific cosmology is usually considered to have begun in
1917 with Albert Einstein's publication of his final modification of
general relativity in the paper "Cosmological Considerations of the
General
TheoryTheory of Relativity" (although this paper was not widely
available outside of Germany until the end of World War I).
General relativityGeneral relativity prompted cosmogonists such as Willem de Sitter,
Karl Schwarzschild, and
Arthur EddingtonArthur Eddington to explore its astronomical
ramifications, which enhanced the ability of astronomers to study very
distant objects. Physicists began changing the assumption that the
UniverseUniverse was static and unchanging. In 1922 Alexander Friedmann
introduced the idea of an expanding universe that contained moving
matter.

In parallel to this dynamic approach to cosmology, one long-standing
debate about the structure of the cosmos was coming to a climax. Mount
Wilson astronomer
Harlow ShapleyHarlow Shapley championed the model of a cosmos made
up of the
Milky WayMilky Way star system only; while
Heber D. CurtisHeber D. Curtis argued for
the idea that spiral nebulae were star systems in their own right as
island universes. This difference of ideas came to a climax with the
organization of the Great Debate on 26 April 1920 at the meeting of
the U.S.
National Academy of SciencesNational Academy of Sciences in
Washington, D.C.Washington, D.C. The debate
was resolved when
Edwin HubbleEdwin Hubble detected
Cepheid VariablesCepheid Variables in the
Andromeda galaxyAndromeda galaxy in 1923 and 1924. Their distance established spiral
nebulae well beyond the edge of the Milky Way.
Subsequent modelling of the universe explored the possibility that the
cosmological constant, introduced by Einstein in his 1917 paper, may
result in an expanding universe, depending on its value. Thus the Big
Bang model was proposed by the Belgian priest
Georges LemaîtreGeorges Lemaître in
1927 which was subsequently corroborated by Edwin Hubble's discovery
of the red shift in 1929 and later by the discovery of the cosmic
microwave background radiation by
Arno PenziasArno Penzias and Robert Woodrow
Wilson in 1964. These findings were a first step to rule out some of
many alternative cosmologies.
Since around 1990, several dramatic advances in observational
cosmology have transformed cosmology from a largely speculative
science into a predictive science with precise agreement between
theory and observation. These advances include observations of the
microwave background from the COBE,
WMAPWMAP and Planck satellites, large
new galaxy redshift surveys including 2dfGRS and SDSS, and
observations of distant supernovae and gravitational lensing. These
observations matched the predictions of the cosmic inflation theory, a
modified
Big BangBig Bang theory, and the specific version known as the
Lambda-CDMLambda-CDM model. This has led many to refer to modern times as the
"golden age of cosmology".[13]
On 17 March 2014, astronomers at the Harvard-Smithsonian Center for
AstrophysicsAstrophysics announced the detection of gravitational waves, providing
strong evidence for inflation and the Big Bang.[10][11][12] However,
on 19 June 2014, lowered confidence in confirming the cosmic inflation
findings was reported.[14][15][16]
On 1 December 2014, at the Planck 2014 meeting in Ferrara, Italy,
astronomers reported that the universe is 13.8 billion years old and
is composed of 4.9% atomic matter, 26.6% dark matter and 68.5% dark
energy.[17]
Religious or mythological cosmology[edit]
See also: Religious cosmology
Religious or mythological cosmology is a body of beliefs based on
mythological, religious, and esoteric literature and traditions of
creation and eschatology.
Philosophical cosmology[edit]
See also:
CosmologyCosmology (philosophy)
CosmologyCosmology deals with the world as the totality of space, time and all
phenomena. Historically, it has had quite a broad scope, and in many
cases was founded in religion.[citation needed] The ancient Greeks did
not draw a distinction between this use and their model for the
cosmos.[citation needed] However, in modern use metaphysical cosmology
addresses questions about the
UniverseUniverse which are beyond the scope of
science. It is distinguished from religious cosmology in that it
approaches these questions using philosophical methods like
dialectics. Modern metaphysical cosmology tries to address questions
such as:[citation needed]

What is the origin of the Universe? What is its first cause? Is its
existence necessary? (see monism, pantheism, emanationism and
creationism)
What are the ultimate material components of the Universe? (see
mechanism, dynamism, hylomorphism, atomism)
What is the ultimate reason for the existence of the Universe? Does
the cosmos have a purpose? (see teleology)
Does the existence of consciousness have a purpose? How do we know
what we know about the totality of the cosmos? Does cosmological
reasoning reveal metaphysical truths? (see epistemology)

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Name
Author and date
Classification
Remarks

Hindu cosmology
RigvedaRigveda (c. 1700–1100 BC)
Cyclical or oscillating, Infinite in time
One cycle of existence is around 311 trillion years and the life of
one universe around 8 billion years. This Universal cycle is preceded
by an infinite number of universes and to be followed by another
infinite number of universes. Includes an infinite number of universes
at one given time.

Jain cosmology
Jain AgamasJain Agamas (written around 500 AD as per the teachings of Mahavira
599–527 BC)
Cyclical or oscillating, eternal and finite
Jain cosmologyJain cosmology considers the loka, or universe, as an uncreated
entity, existing since infinity, the shape of the universe as similar
to a man standing with legs apart and arm resting on his waist. This
Universe, according to Jainism, is broad at the top, narrow at the
middle and once again becomes broad at the bottom.

Babylonian cosmology
Babylonian literature (c. 3000 BC)
Flat earth floating in infinite "waters of chaos"
The Earth and the Heavens form a unit within infinite "waters of
chaos"; the earth is flat and circular, and a solid dome (the
"firmament") keeps out the outer "chaos"-ocean.

Biblical cosmology
Genesis creation narrative
Earth floating in infinite "waters of chaos"
The Earth and the Heavens form a unit within infinite "waters of
chaos"; the "firmament" keeps out the outer "chaos"-ocean.

Atomist universe
AnaxagorasAnaxagoras (500–428 BC) & later Epicurus
Infinite in extent
The universe contains only two things: an infinite number of tiny
seeds (atoms) and the void of infinite extent. All atoms are made of
the same substance, but differ in size and shape. Objects are formed
from atom aggregations and decay back into atoms. Incorporates
Leucippus' principle of causality: "nothing happens at random;
everything happens out of reason and necessity". The universe was not
ruled by gods.[citation needed]

Pythagorean universe
PhilolausPhilolaus (d. 390 BC)
Existence of a "Central Fire" at the center of the Universe.
At the center of the
UniverseUniverse is a central fire, around which the
Earth, Sun,
MoonMoon and planets revolve uniformly. The
SunSun revolves
around the central fire once a year, the stars are immobile. The earth
in its motion maintains the same hidden face towards the central fire,
hence it is never seen. First known non-geocentric model of the
Universe.[18]

De Mundo
Pseudo-
AristotleAristotle (d. 250 BC or between 350 and 200 BC)
The
UniverseUniverse then is a system made up of heaven and earth and the
elements which are contained in them.
There are "five elements, situated in spheres in five regions, the
less being in each case surrounded by the greater — namely, earth
surrounded by water, water by air, air by fire, and fire by ether —
make up the whole Universe."[19]

Stoic universe
StoicsStoics (300 BC – 200 AD)
Island universe
The cosmos is finite and surrounded by an infinite void. It is in a
state of flux, and pulsates in size and undergoes periodic upheavals
and conflagrations.

Aristarchean universe
Aristarchus (circa 280 BC)
Heliocentric
Earth rotates daily on its axis and revolves annually about the sun in
a circular orbit. Sphere of fixed stars is centered about the sun.

Ptolemaic model
PtolemyPtolemy (2nd century AD)
GeocentricGeocentric (based on Aristotelian universe)
UniverseUniverse orbits around a stationary Earth. Planets move in circular
epicycles, each having a center that moved in a larger circular orbit
(called an eccentric or a deferent) around a center-point near Earth.
The use of equants added another level of complexity and allowed
astronomers to predict the positions of the planets. The most
successful universe model of all time, using the criterion of
longevity.
AlmagestAlmagest (the Great System).

Aryabhatan model
AryabhataAryabhata (499)
GeocentricGeocentric or Heliocentric
The Earth rotates and the planets move in elliptical orbits around
either the Earth or Sun; uncertain whether the model is geocentric or
heliocentric due to planetary orbits given with respect to both the
Earth and Sun.

Medieval universe
Medieval philosophers (500–1200)
Finite in time
A universe that is finite in time and has a beginning is proposed by
the Christian philosopher John Philoponus, who argues against the
ancient Greek notion of an infinite past. Logical arguments supporting
a finite universe are developed by the early Muslim philosopher
Alkindus, the Jewish philosopher Saadia Gaon, and the Muslim
theologian Algazel.

Multiversal cosmology
Fakhr al-Din al-Razi (1149–1209)
Multiverse, multiple worlds and universes
There exists an infinite outer space beyond the known world, and God
has the power to fill the vacuum with an infinite number of universes.

Maragha models
Maragha school (1259–1528)
Geocentric
Various modifications to Ptolemaic model and Aristotelian universe,
including rejection of equant and eccentrics at Maragheh observatory,
and introduction of
Tusi-coupleTusi-couple by Al-Tusi. Alternative models later
proposed, including the first accurate lunar model by Ibn al-Shatir, a
model rejecting stationary Earth in favour of
Earth's rotationEarth's rotation by Ali
Kuşçu, and planetary model incorporating "circular inertia" by
Al-Birjandi.

Nilakanthan model
Nilakantha Somayaji (1444–1544)
GeocentricGeocentric and heliocentric
A universe in which the planets orbit the Sun, which orbits the Earth;
similar to the later Tychonic system

Bruno's cosmology
Giordano BrunoGiordano Bruno (1548–1600)
Infinite extent, infinite time, homogeneous, isotropic,
non-hierarchical
Rejects the idea of a hierarchical universe. Earth and
SunSun have no
special properties in comparison with the other heavenly bodies. The
void between the stars is filled with aether, and matter is composed
of the same four elements (water, earth, fire, and air), and is
atomistic, animistic and intelligent.

Keplerian
Johannes KeplerJohannes Kepler (1571–1630)
HeliocentricHeliocentric with elliptical planetary orbits
Kepler's discoveries, marrying mathematics and physics, provided the
foundation for our present conception of the Solar system, but distant
stars were still seen as objects in a thin, fixed celestial sphere.

Static Newtonian
Isaac NewtonIsaac Newton (1642–1727)
Static (evolving), steady state, infinite
Every particle in the universe attracts every other particle. Matter
on the large scale is uniformly distributed. Gravitationally balanced
but unstable.

Cartesian Vortex universe
René Descartes, 17th century
Static (evolving), steady state, infinite
System of huge swirling whirlpools of aethereal or fine matter
produces what we would call gravitational effects. But his vacuum was
not empty; all space was filled with matter.

Curvature constant k = 0. Said to be infinite (but ambiguous).
"Unbounded cosmos of limited extent". Expands forever. "Simplest" of
all known universes. Named after but not considered by Friedmann. Has
a deceleration term q =½, which means that its expansion rate slows
down.

Λ is positive and has a magnitude greater than gravity.
UniverseUniverse has
initial high-density state ("primeval atom"). Followed by a two-stage
expansion. Λ is used to destabilize the universe. (Lemaître is
considered the father of the big bang model.)

Oscillating universeOscillating universe (Friedmann-Einstein)
Favored by Friedmann, 1920s
Expanding and contracting in cycles
Time is endless and beginningless; thus avoids the beginning-of-time
paradox. Perpetual cycles of big bang followed by big crunch.
(Einstein's first choice after he rejected his 1917 model.)

Kinematic expansion without space expansion
Rejects general relativity and the expanding space paradigm. Gravity
not included as initial assumption. Obeys cosmological principle and
special relativity; consists of a finite spherical cloud of particles
(or galaxies) that expands within an infinite and otherwise empty flat
space. It has a center and a cosmic edge (surface of the particle
cloud) that expands at light speed. Explanation of gravity was
elaborate and unconvincing.

Friedmann–Lemaître–Robertson–WalkerFriedmann–Lemaître–Robertson–Walker class of models
Howard Robertson, Arthur Walker, 1935
Uniformly expanding
Class of universes that are homogeneous and isotropic. Spacetime
separates into uniformly curved space and cosmic time common to all
co-moving observers. The formulation system is now known as the FLRW
or Robertson–Walker metrics of cosmic time and curved space.

Ambiplasma
Hannes AlfvénHannes Alfvén 1965 Oskar Klein
Cellular universe, expanding by means of matter–antimatter
annihilation
Based on the concept of plasma cosmology. The universe is viewed as
"meta-galaxies" divided by double layers and thus a bubble-like
nature. Other universes are formed from other bubbles. Ongoing cosmic
matter-antimatter annihilations keep the bubbles separated and moving
apart preventing them from interacting.

Cosmic inflation
Alan GuthAlan Guth 1980
Big BangBig Bang modified to solve horizon and flatness problems
Based on the concept of hot inflation. The universe is viewed as a
multiple quantum flux—hence its bubble-like nature. Other universes
are formed from other bubbles. Ongoing cosmic expansion kept the
bubbles separated and moving apart.